libexpr-c: fix changing eval settings having no effect

src/libcmd/common-eval-args.cc

@@ -19,13 +19,8 @@
 
 namespace nix {
 
-fetchers::Settings fetchSettings;
-
-static GlobalConfig::Register rFetchSettings(&fetchSettings);
-
-EvalSettings evalSettings{
-    settings.readOnlyMode,
-    {
+static GlobalConfig::Register rEvalSettings(&evalSettings, [] {
+    evalSettings.lookupPathHooks = {
         {
             "flake",
             [](EvalState & state, std::string_view rest) {
@@ -45,10 +40,8 @@ EvalSettings evalSettings{
                 return state.storePath(storePath);
             },
         },
-    },
-};
-
-static GlobalConfig::Register rEvalSettings(&evalSettings);
+    };
+});
 
 flake::Settings flakeSettings;
 

src/libexpr-c/nix_api_expr.cc

@@ -6,6 +6,7 @@
 #include "nix/expr/eval-gc.hh"
 #include "nix/store/globals.hh"
 #include "nix/expr/eval-settings.hh"
+#include "nix/fetchers/fetch-settings.hh"
 #include "nix/util/ref.hh"
 
 #include "nix_api_expr.h"
@@ -132,8 +133,8 @@ nix_eval_state_builder * nix_eval_state_builder_new(nix_c_context * context, Sto
         return unsafe_new_with_self<nix_eval_state_builder>([&](auto * self) {
             return nix_eval_state_builder{
                 .store = nix::ref<nix::Store>(store->ptr),
-                .settings = nix::EvalSettings{/* &bool */ self->readOnlyMode},
-                .fetchSettings = nix::fetchers::Settings{},
+                .settings = &nix::evalSettings,
+                .fetchSettings = &nix::fetchSettings,
                 .readOnlyMode = true,
             };
         });
@@ -154,9 +155,9 @@ nix_err nix_eval_state_builder_load(nix_c_context * context, nix_eval_state_buil
         context->last_err_code = NIX_OK;
     try {
         // TODO: load in one go?
-        builder->settings.readOnlyMode = nix::settings.readOnlyMode;
-        loadConfFile(builder->settings);
-        loadConfFile(builder->fetchSettings);
+        builder->settings->readOnlyMode = nix::settings.readOnlyMode;
+        loadConfFile(*builder->settings);
+        loadConfFile(*builder->fetchSettings);
     }
     NIXC_CATCH_ERRS
 }
@@ -183,9 +184,9 @@ EvalState * nix_eval_state_build(nix_c_context * context, nix_eval_state_builder
     try {
         return unsafe_new_with_self<EvalState>([&](auto * self) {
             return EvalState{
-                .fetchSettings = std::move(builder->fetchSettings),
-                .settings = std::move(builder->settings),
-                .state = nix::EvalState(builder->lookupPath, builder->store, self->fetchSettings, self->settings),
+                .fetchSettings = builder->fetchSettings,
+                .settings = builder->settings,
+                .state = nix::EvalState(builder->lookupPath, builder->store, *self->fetchSettings, *self->settings),
             };
         });
     }

src/libexpr-c/nix_api_expr_internal.h

@@ -13,17 +13,17 @@ extern "C" {
 struct nix_eval_state_builder
 {
     nix::ref<nix::Store> store;
-    nix::EvalSettings settings;
-    nix::fetchers::Settings fetchSettings;
+    nix::EvalSettings * settings;
+    nix::fetchers::Settings * fetchSettings;
     nix::LookupPath lookupPath;
     // TODO: make an EvalSettings setting own this instead?
     bool readOnlyMode;
 };
 
 struct EvalState
 {
-    nix::fetchers::Settings fetchSettings;
-    nix::EvalSettings settings;
+    nix::fetchers::Settings * fetchSettings;
+    nix::EvalSettings * settings;
     nix::EvalState state;
 };
 

src/libexpr/eval-settings.cc

@@ -1,4 +1,5 @@
 #include "nix/util/users.hh"
+#include "nix/util/config-global.hh"
 #include "nix/store/globals.hh"
 #include "nix/store/profiles.hh"
 #include "nix/expr/eval.hh"
@@ -108,4 +109,8 @@ std::filesystem::path getNixDefExpr()
     return settings.useXDGBaseDirectories ? getStateDir() / "defexpr" : getHome() / ".nix-defexpr";
 }
 
+EvalSettings evalSettings{settings.readOnlyMode};
+
+static GlobalConfig::Register rEvalSettings(&evalSettings);
+
 } // namespace nix

src/libexpr/include/nix/expr/eval-settings.hh

@@ -368,4 +368,9 @@ struct EvalSettings : Config
  */
 std::filesystem::path getNixDefExpr();
 
+/**
+ * EvalSettings instance from libexpr.
+ */
+extern EvalSettings evalSettings;
+
 } // namespace nix

src/libfetchers/fetch-settings.cc

@@ -1,7 +1,16 @@
 #include "nix/fetchers/fetch-settings.hh"
+#include "nix/util/config-global.hh"
 
 namespace nix::fetchers {
 
 Settings::Settings() {}
 
 } // namespace nix::fetchers
+
+namespace nix {
+
+fetchers::Settings fetchSettings;
+
+static GlobalConfig::Register rFetchSettings(&fetchSettings);
+
+} // namespace nix

src/libfetchers/include/nix/fetchers/fetch-settings.hh

@@ -138,3 +138,12 @@ private:
 };
 
 } // namespace nix::fetchers
+
+namespace nix {
+
+/**
+ * @todo Get rid of global settings variables
+ */
+extern fetchers::Settings fetchSettings;
+
+} // namespace nix

src/libflake-c/nix_api_flake.cc

@@ -32,7 +32,7 @@ nix_err nix_flake_settings_add_to_eval_state_builder(
 {
     nix_clear_err(context);
     try {
-        settings->settings->configureEvalSettings(builder->settings);
+        settings->settings->configureEvalSettings(*builder->settings);
     }
     NIXC_CATCH_ERRS
 }

src/libutil/config-global.cc

@@ -61,7 +61,16 @@ GlobalConfig globalConfig;
 
 GlobalConfig::Register::Register(Config * config)
 {
-    configRegistrations().emplace_back(config);
+    auto regs = configRegistrations();
+    if (std::find(regs.begin(), regs.end(), config) == regs.end()) {
+        configRegistrations().emplace_back(config);
+    }
+}
+
+GlobalConfig::Register::Register(Config * config, std::function<void()> && callback)
+    : Register(config)
+{
+    callback();
 }
 
 ExperimentalFeatureSettings experimentalFeatureSettings;

src/libutil/include/nix/util/config-global.hh

@@ -26,6 +26,7 @@ struct GlobalConfig : public AbstractConfig
     struct Register
     {
         Register(Config * config);
+        Register(Config * config, std::function<void()> && callback);
     };
 };